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On Combustion in the CNG-Diesel Dual Fuel Engine
KTH, School of Industrial Engineering and Management (ITM), Machine Design (Dept.), Internal Combustion Engines.
2014 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Currently there is a large interest in alternative transport fuels. There are two underlying reasons for this interest: the desire to decrease the environmental impact of transports and the need to compensate for the declining availability of petroleum. In the light of both these factors, the CNG-diesel dual fuelengine is an attractive concept. The primary fuel of the dual fuel engine is methane, which can be derived both from renewables and from fossil sources. Methane from organic waste, commonly referred to as biomethane, can provide a reduction in greenhouse gases unmatched by any other fuel. Furthermore, fossil methane, natural gas, is one of the most abundant fossil fuels.Thedual fuelengine is, from a combustion point of view, a hybridof the diesel and theOtto-engineand it shares characteristics with both.

From a market standpoint, the dual fuel technology is highly desirable; however, from a technical point of view it has proven difficult to realize. The aim of this project was to identify limitations to engine operation, investigate these challenges, and ,as much as possible, suggest remedies. Investigations have been made into emissions formation, nozzle-hole coking, impact of varying in-cylinder air motion, behavior and root causes of pre-ignitions, and the potential of advanced injection strategies and unconventional combustion modes. The findings from each of these investigations have been summarized, and recommendations for the development of a Euro 6 compliant dual fuel engine have been formulated. Two key challenges must be researched further for this development to succeed: an aftertreatment system which allows for low exhaust temperatures must be available, and the root cause of pre-ignitions must be found and eliminated.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2014. , x, 98 p.
Series
TRITA-MMK, ISSN 1400-1179 ; 2014:08
National Category
Energy Engineering
Research subject
Machine Design
Identifiers
URN: urn:nbn:se:kth:diva-151188ISBN: 978-91-7595-243-7 (print)OAI: oai:DiVA.org:kth-151188DiVA: diva2:747001
Public defence
2014-09-26, Kollegiesalen, Brinellvägen 8, KTH, Stockholm, 14:00 (English)
Opponent
Supervisors
Funder
Swedish Energy Agency
Note

QQC 20140915

Available from: 2014-09-15 Created: 2014-09-15 Last updated: 2014-09-15Bibliographically approved
List of papers
1. Combustion Modes in a Diesel-CNG Dual Fuel Engine
Open this publication in new window or tab >>Combustion Modes in a Diesel-CNG Dual Fuel Engine
2011 (English)In: SAE Technical Paper 2011-01-1962, 2011, Society of Automotive Engineers of Japan, Inc , 2011, 2387-2398 p.Conference paper, Published paper (Refereed)
Abstract [en]

Diesel Dual Fuel, DDF, is a concept where a combination of methane and diesel is used in a compression ignited engine, maintaining the high compression ratio of a diesel engine with the resulting benefits in thermal efficiency.

One benefit of having two fuels on board the vehicle is the additional degree of freedom provided by the ratio between the fuels. This additional degree of freedom enables control of combustion phasing for combustion modes such as Homogenous Charge Compression Ignition, HCCI, and Partly Premixed Compression Ignition, PPCI. These unconventional combustion modes have great potential to limit emissions at light load while maintaining the low pumping losses of the base diesel engine.

A series of tests has been carried out on a single cylinder lab engine, equipped with a modern common rail injection system supplying the diesel fuel and two gas injectors, placed in the intake runners. Four load points are investigated and three different types of combustion are evaluated.

The study confirmed the desirable emission characteristics of HCCI and PPCI combustion and demonstrated the potential to control the combustion phasing by utilizing all degrees of freedom provided by a common rail injection system and two fuels.

Place, publisher, year, edition, pages
Society of Automotive Engineers of Japan, Inc, 2011
Keyword
Diesel Dual Fuel, Biogas, DDF, CNG, methane, HCCI, PPC, PPCI, RCCI, Förbränningsmotorteknik, metan
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-65693 (URN)10.4271/2011-01-1962 (DOI)2-s2.0-84881193912 (Scopus ID)
Conference
JSAE Powertrains, Fuels & Lubricants
Projects
Diesel Dual Fuel
Note
QC 20120202Available from: 2012-02-02 Created: 2012-01-25 Last updated: 2014-09-15Bibliographically approved
2. Characterization and Potential of Dual FuelCombustion in a Modern Diesel Engine
Open this publication in new window or tab >>Characterization and Potential of Dual FuelCombustion in a Modern Diesel Engine
2011 (English)In: SAE Technical Paper 2011-01-2223, SAE International , 2011Conference paper, Published paper (Refereed)
Abstract [en]

Diesel Dual Fuel, DDF, is a concept which promises the possibility to utilize CNG/biogas in a compression ignition engine maintaining a high compression ratio, made possible by the high knock resistance of methane, and the resulting benefits in thermal efficiency associated with Diesel combustion.

A series of tests has been carried out on a single cylinder lab engine, equipped with a modern common rail injection system supplying the diesel fuel and two gas injectors, placed in the intake runners. One feature of port injected Dual Fuel is that full diesel functionality is maintained, which is of great importance when bringing the dual fuel technology to market. The objective of the study was to characterize and investigate the potential for dual fuel combustion utilizing all degrees of freedom available in a modern diesel engine.

Increased diesel pilot proved efficient at reducing NOx emissions at low λ. Advanced combustion phasing has the potential to extend the lean limit for operation. Stoichiometric operation using high levels of EGR is identified as a promising field in conjunction with raised inlet temperature.

Place, publisher, year, edition, pages
SAE International, 2011
Keyword
Diesel Dual Fuel, Biogas, DDF, CNG, methane, Förbränningsmotorteknik, Biogas, metan
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-65727 (URN)10.4271/2011-01-2223 (DOI)2-s2.0-84877548364 (Scopus ID)
Conference
Commercial Vehicle Engineering Congress, September 2011, Chicago
Projects
Diesel Dual Fuel
Note
QC 20120202Available from: 2012-02-02 Created: 2012-01-25 Last updated: 2014-09-15Bibliographically approved
3. Controlling the Injector Tip Temperature in a DieselDual Fuel Engine
Open this publication in new window or tab >>Controlling the Injector Tip Temperature in a DieselDual Fuel Engine
2012 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Diesel Dual Fuel, DDF, is a concept where a combination of methane and diesel is used in a compression ignited engine, maintaining the high compression ratio of a diesel engine with the resulting benefits in thermal efficiency. Attention has recently been drawn to the fact that the tip of the diesel injector may reach intolerable temperatures. The high injector tip temperatures in the DDF engine are caused by the reduction in diesel flow through the injector. For dual fuel operation, as opposed to diesel, high load does not necessarily imply a high flow of diesel through the injector nozzle.

This research investigated the factors causing high injector tip temperatures in a DDF engine and the underlying mechanisms which transfer heat to and from the injector tip. Parameter sweeps of each influential parameter were carried out and evaluated. In addition to this, a simple and useful model was constructed based on the heat balance of the injector tip.

Decreasing the thermal resistance between the injector tip and the cooling water by inserting a copper sleeve around the injector tip has the potential to greatly reduce the injector tip temperature and effectively remove it as a limiting factor.

Place, publisher, year, edition, pages
SAE International, 2012
Keyword
Diesel Dual Fuel, CNG, Methane, Biogas, Alternative fuels, injector, coking, overheating
National Category
Vehicle Engineering
Identifiers
urn:nbn:se:kth:diva-96943 (URN)10.4271/2012-01-0826 (DOI)2-s2.0-84877181760 (Scopus ID)
Conference
SAE World Congress, April 24-26, 2012, Detroit, Michigan, USA
Projects
Diesel Dual Fuel
Note
QC 20120613Available from: 2012-06-13 Created: 2012-06-13 Last updated: 2014-09-15Bibliographically approved
4. The Influence of Crevices on Hydrocarbon Emissions from a Diesel-Methane Dual Fuel Engine
Open this publication in new window or tab >>The Influence of Crevices on Hydrocarbon Emissions from a Diesel-Methane Dual Fuel Engine
2013 (English)In: SAE International Journal of Engines, ISSN 1946-3936, Vol. 6, no 2, 751-765 p.Article in journal (Refereed) Published
Abstract [en]

Emissions of unburned methane are the Achilles heel of premixed gas engines whether they are spark ignited or diesel pilot ignited. If the engine is operated lean, lower temperatures prevail in the combustion chamber and several of the mechanisms behind the hydrocarbon emissions are aggravated. This paper presents an experimental investigation of the contribution from combustion chamber crevices and quenching to the total hydrocarbon emissions from a diesel-methane dual fuel engine at different operating conditions and air excess ratios. It is shown that the sensitivity to a change in topland crevice volume is greater at lean conditions than at stoichiometry. More than 70% of hydrocarbon emissions at air excess ratios relevant to operation of lean burn engines can be attributed to crevices.

Keyword
Crevice volumes, Different operating conditions, Experimental investigations, Hydrocarbon emission, Lean condition, Lean-burn engines, Lower temperatures, Total hydrocarbons
National Category
Vehicle Engineering Energy Engineering
Identifiers
urn:nbn:se:kth:diva-134248 (URN)10.4271/2013-01-0848 (DOI)2-s2.0-84878793872 (Scopus ID)
Funder
Swedish Energy Agency
Note

QC 20140304

Available from: 2013-11-21 Created: 2013-11-20 Last updated: 2014-09-15Bibliographically approved
5. The Influence of In-Cylinder Flows on Emissions and Heat Transfer from Methane-Diesel Dual Fuel Combustion
Open this publication in new window or tab >>The Influence of In-Cylinder Flows on Emissions and Heat Transfer from Methane-Diesel Dual Fuel Combustion
2013 (English)In: SAE International Journal of Engines, ISSN 1946-3936, Vol. 6, no 4Article in journal (Refereed) Published
Abstract [en]

In order for premixed methane diesel dual fuel engines to meet current and future legislation, the emissions of unburned hydrocarbons must be reduced while high efficiency and high methane utilization is maintained. This paper presents an experimental investigation into the effects of in cylinder air motion, swirl and tumble, on the emissions, heat transfer and combustion characteristics of dual fuel combustion at different air excess ratios. Measurements have been carried out on a single cylinder engine equipped with a fully variable valve train, Lotus AVT. By applying different valve lift profiles for the intake valves, the swirl was varied between 0.5 and 6.5 at BDC and the tumble between 0.5 and 4 at BDC. A commercial 1D engine simulation tool was used to calculate swirl number and tumble for the different valve profiles. Input data for the simulation software was generated using a steady-state flow rig with honeycomb torque measurements. To measure heat transfer, thermocouples were fitted in the cylinder head and heat exchangers on the coolant circuit and the engine oil. The study shows that swirl has a strong effect on the heat transfer; increasing the swirl from 0.5 to 6.5 increases the heat transfer to the coolant by 50%. With regards to emissions; swirl has the effect of increasing oxidation of hydrocarbons returning from crevices. For this reason a 20% reduction of hydrocarbon emissions can be achieved by increasing the swirl from 0.4 to 3. At high λ of 1.9, combustion is very sensitive to mixing between the gas and the air. The mixing is affected by the turbulence generated over the intake valves. A difference in engine out HC emissions by a factor of two can be achieved by varying the valve lift curve and hence varying the turbulence generated during the intake event. The timing of the gas injection can also improve mixing and achieve similar results. Compared to SI, dual fuel combustion is relatively insensitive to tumble.

Keyword
Combustion characteristics, Different valve lift, Experimental investigations, Hydrocarbon emission, In-cylinder air motions, Single cylinder engine, Unburned hydrocarbons, Variable valve train, Combustion, Computer software, Coolants, Dual fuel engines, Heat transfer, Intake valves, Methane, Mixing, Thermocouples, Turbulence, Engine cylinders
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-140058 (URN)10.4271/2013-01-2509 (DOI)2-s2.0-84886613446 (Scopus ID)
Note

QC 20140117

Available from: 2014-01-17 Created: 2014-01-16 Last updated: 2014-09-15Bibliographically approved
6. Nozzle Coking in CNG-Diesel Dual Fuel Engines: 2014-01-2700
Open this publication in new window or tab >>Nozzle Coking in CNG-Diesel Dual Fuel Engines: 2014-01-2700
2014 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Nozzle coking in diesel engines has received a lot of attention in recent years. High temperature in the nozzle tip is one of the key factors known to accelerate this process. In premixed CNG-diesel dual fuel, DDF, engines a large portion of the diesel fuel through the injector is removed compared to regular diesel operation. This can result in very high nozzle temperatures. Nozzle hole coking can therefore be expected to pose a significant challenge for DDF operation.In this paper an experimental study of nozzle coking has been performed on a DDF single cylinder engine. The objective was to investigate how the rate of injector nozzle hole coking during DDF operation compares to diesel operation. In addition to the nozzle tip temperature, the impact of other parameters on coking rate was also of interest.Start of injection, λ, diesel substitution ratio and common rail pressure were varied in two levels starting from a common baseline case, resulting in a total of 10 operating cases. These cases were run for three and a half hours in steady-state, using standard injectors and zinc contaminated diesel to accelerate the coking process. The zinc was added in form of zinc neodecanoate, similar to the practice in the standardized tests used to study nozzle coking in diesel engines.After the tests the injectors were disassembled and the steady state flow through the injector nozzles was measured to isolate the effect of nozzle hole coking. The results show significant coking from only a few hours of testing. The most challenging case was the combination of high nozzle tip temperature from DDF operation with low injection pressure. The flow loss from operation in DDF mode was far more severe compared to diesel operation. Elemental analysis of the deposits shows similar composition resulting from diesel and DDF operation. In the DDF deposits higher concentrations of elements from the engine oil were found in addition to higher carbon content. It is concluded that injector nozzle coking is a challenge which requires appropriate attention when developing DDF engines.

National Category
Energy Engineering
Research subject
Machine Design
Identifiers
urn:nbn:se:kth:diva-151190 (URN)
Conference
SAE Powertrains, Fuels & Lubes 2014
Funder
Swedish Energy Agency
Note

QC 20140915

Available from: 2014-09-15 Created: 2014-09-15 Last updated: 2014-09-15Bibliographically approved

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Output format
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